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View Poll Results: Pumping; is it bad?
Won't hurt the car 12 41.38%
DON'T DO IT! 17 58.62%
Voters: 29. You may not vote on this poll

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Old 05-12-2007, 12:00 AM   #1
Lord Odin
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Default Pumping gas pedal when starting car w/ fuel injection

I have heard that pumping the gas pedal when a car that has fuel injection and is having trouble starting is bad for the car. No explanation as to why but only that it is bad and fuel injection should handle the problem by itself, unlike vehicles with carburetors. What is so bad about pumping the gas?

If the injectors are getting clogged, wouldn't pumping the pedal actually help it in that circumstance?
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Old 05-12-2007, 12:08 AM   #2
CGGorman
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In some case, the ECU will shut down the injectors if you WOT during cranking. This is a routine inserted to help clear a flooded engine.

Oherwise, I don't know a reason why pumping would help OR hurt.
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Old 05-12-2007, 12:16 AM   #3
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Injectors are basically just electric switches. They either spray or not, depending on te presence of electrical current. The only real variable with a given injector is how long the "switch" is allowed to remain off or on. The throttle in most EFI car until very recently was electromechanical. Mech. in that it opened and closed the throttle blades just like on a carb. Electrical in that there is a sensor mounted on the throttle butterfly shaft that tells the computer how far open the throttle is. The computer uses that info, plus more info from various other sensors (air flow, air temp, crank position+RPM, etc.) to determine how to switch the injectors.

Pumping the throttle is useless in a EFI engine. If it won't start, there is a real problem somewhere.

On a carbureted engine, your foot controls a helluva lot more, such as the choke position and enrichment (squirt of raw fuel for each press of the pedal). The fuel delivery is "dumb". It relies completely upon engine vacuum or your foot (or both) to get fuel out of the fuel bowl.

A cold engine needs a richer mixture to start and run smoothly. On EFI cars, that is handled by the computers. On Carb'd engines, it's the choke. Most people don't have a freakin' clue how to tune a carb to run when the engine is warm, let alone when it's cold or during the transition between the two. Often, that means not enough fuel during cold start, so pumping the throttle will squort a bunch extra in there. It will just lay in the intake for a bit, but it;s enough to get the car running.

Last edited by CGGorman; 05-12-2007 at 12:31 AM.
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Old 05-12-2007, 12:20 AM   #4
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Quote:
Originally Posted by Lord Odin View Post
I have heard that pumping the gas pedal when a car that has fuel injection and is having trouble starting is bad for the car. No explanation as to why but only that it is bad and fuel injection should handle the problem by itself, unlike vehicles with carburetors. What is so bad about pumping the gas?

If the injectors are getting clogged, wouldn't pumping the pedal actually help it in that circumstance?
My answer is Both. It won't really hurt the car (may flood) but I don't do it.
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Old 05-12-2007, 12:20 AM   #5
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Quote:
Originally Posted by CGGorman View Post
In some case, the ECU will shut down the injectors if you WOT during cranking. This is a routine inserted to help clear a flooded engine.

Oherwise, I don't know a reason why pumping would help OR hurt.
Exactly. There's no point to pump the pedal on a fuel injected car UNLESS you know the engine is flooded and you need to clear out the cylinders. Even in that case you simply hold the pedal to the floor until the car starts.
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Old 05-12-2007, 12:31 AM   #6
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Originally Posted by Fastbird93 View Post
Exactly. There's no point to pump the pedal on a fuel injected car UNLESS you know the engine is flooded and you need to clear out the cylinders. Even in that case you simply hold the pedal to the floor until the car starts.
Most injected cars have a "clear flood mode". If you hold the pedal down all the way and then crank the car, the injectors do not squirt fuel.
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Old 05-12-2007, 12:32 AM   #7
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C4s put you into a flood clear mode and don't fire the injectors with the pedal at WOT during cranking.
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Old 05-12-2007, 12:36 AM   #8
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best to try to start 3 times (short cranks) No start smell for fuel,,,turn key on press one time then crank
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Old 05-12-2007, 01:56 AM   #9
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Quote:
Originally Posted by CGGorman View Post
Injectors are basically just electric switches. They either spray or not, depending on te presence of electrical current. The only real variable with a given injector is how long the "switch" is allowed to remain off or on. The throttle in most EFI car until very recently was electromechanical. Mech. in that it opened and closed the throttle blades just like on a carb. Electrical in that there is a sensor mounted on the throttle butterfly shaft that tells the computer how far open the throttle is. The computer uses that info, plus more info from various other sensors (air flow, air temp, crank position+RPM, etc.) to determine how to switch the injectors.

Pumping the throttle is useless in a EFI engine. If it won't start, there is a real problem somewhere.

On a carbureted engine, your foot controls a helluva lot more, such as the choke position and enrichment (squirt of raw fuel for each press of the pedal). The fuel delivery is "dumb". It relies completely upon engine vacuum or your foot (or both) to get fuel out of the fuel bowl.

A cold engine needs a richer mixture to start and run smoothly. On EFI cars, that is handled by the computers. On Carb'd engines, it's the choke. Most people don't have a freakin' clue how to tune a carb to run when the engine is warm, let alone when it's cold or during the transition between the two. Often, that means not enough fuel during cold start, so pumping the throttle will squort a bunch extra in there. It will just lay in the intake for a bit, but it;s enough to get the car running.
What he said.
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Old 05-12-2007, 07:46 AM   #10
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So there is no possible way of pumping the gas pedal to hurt the car with EFI?
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Old 05-12-2007, 07:56 AM   #11
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If you're wanting to pump the pedal due to problems starting a cold vehicle try turning the key to the on position and waiting a few seconds for the fuel pump to pressurize the system before cranking it over.
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Old 05-12-2007, 08:34 AM   #12
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You don't need to touch the gas pedal when starting a fuel injected car.
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Old 05-12-2007, 09:27 AM   #13
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What CGGorman said with one small addition:On a MAF car the ECM, through the TPS, reads not only how far the throttle plates are open but also the rate at which the opening is changing. If you pump the gas pedal while the car is starting the ECM can, in a sense,become confused.
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Old 05-12-2007, 09:27 AM
 
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